1. Field of the Invention
The present invention concerns a one-piece battery comprising a device adapted to measure the temperature of the electrode assemblies contained in the compartments of the battery.
2. Description of the Prior Art
In a one-piece design the cells of the battery are contained in the compartments of a single container separated by partitions. The container is generally made of a plastics material and prism-shaped. Each cell comprises an electrode assembly of alternating positive and negative electrodes separated from each other by a separator.
The temperature of the electrode assembly varies during successive charging and discharging cycles. The charging (or discharging) time can be monitored by measuring the temperature. The accuracy with which the end of charging is detected depends on the quality of the temperature measurement. This reduces overcharging and extends the service life of the battery. Also, if a malfunction occurs the temperature of the electrode assembly can rise suddenly. The safety of the user depends on how quickly the thermal anomaly can be detected. Also, a one-piece battery is generally associated with a cooling device whose efficiency must be monitored.
The measurement is routinely performed by a temperature sensor fixed to one of the external faces of the one-piece battery by an adhesive. A sensor located in this position cannot measure the real temperature of the electrode assemblies and is exposed to all the thermal disturbances external to the battery. There is also the risk of the sensor becoming detached from the wall of the container.
Document EP-0 638 951 describes a one-piece battery to which an end compartment is added to accommodate a safety device including a temperature sensor. The sensor is supported by a lipped member upstanding from the partition separating the end compartment from the adjacent compartment containing an electrode assembly. This arrangement has a number of drawbacks. Firstly, the accuracy with which the temperature is measured in this way is insufficient. In this position the compartment at the end of the battery is exposed to external temperature variations. The sensor reacts to variations in the temperature of the adjacent electrode assembly but it is less sensitive to the temperature of the other electrode assemblies. Secondly, temperature variations are detected with a time-delay. The thermal path between the electrode assembly and the sensor is long, especially for the electrode assemblies at the other end of the battery. Adding the end compartment significantly increases the overall size of the battery and reduces its capacity per unit volume.
Document EP-0 739 048 proposes placing a temperature sensor in an orifice terminating near the upper part of the electrode assembly, the orifice being closed off by an adhesive. The distance between the sensor and the upper part of the electrode assembly can vary according to the dimensional tolerances for the height of the electrodes. Although this arrangement can measure a temperature very close to the real temperature of the electrode assembly, heat transfer only by radiation cannot detect temperature variations with sufficient accuracy. The composition of the gas mixture above the electrode assembly varies during cycling, is richer in hydrogen at the end of charging and can change if the relief valve opens. The volume occupied by the temperature measuring device is still too great.
There is a need for a one-piece battery with a capacity per unit volume at least equal to that of existing batteries and with an extended service life. The battery must also be safer for users.
An aim of the present invention is to propose a one-piece battery including a smaller device for measuring the temperature of the electrode assemblies so that the internal temperature is measured and its variations are monitored more reliably, faster and more accurately than in prior art batteries.